The present invention relates to a method of producing a particulate polymer.
Particulate polymers are intended for use as matting agents for paints, additives to suede- or velvet-texture coatings, cosmetic products, agrochemicals, drugs, etc. and it is foreseen that these polymers will find application in a still greater variety of fields in the years to come.
Among the known manufacturing methods for particulate polymers are the method which comprises reacting a polyester or polyether with an isocyanate in the presence of an oil-modified alkyd resin in a solvent (Japanese Patent Publication No. 50-8116) and the method which comprises the steps of emulsifying a mixture of a polyol and a polyisocyanate in the presence of an emulsifier and a protective colloid in water and, then, adding a polyamine or a catalyst (Japanese Patent Publication No. 51-34880, No. 51-10878 and No. 56-9531).
In these known manufacturing technologies for particulate polymers, it is essential to add an oil-soluble or water-soluble protective colloid, such as oil-modified alkyd resin, polyvinyl alcohol, gelatin or the like, in order to preclude aggregation of particles during the curing reaction.
However, the addition of such of protective colloid results in the following disadvantages.
(1) Owing to the thickening or viscosity-building effect of the protective colloid, the recovery step after production of particles requires a prolonged filtration or centrifugation procedure and, in worst cases, the recovery becomes substantially impossible.
(2) In drying the separated particles to obtain a powder, if the particles are directly dried without washing, the protective colloid remaining on and between the particles forms a film to interconnect the particles, thus preventing effective reduction to a powder. For the removal of the protective colloid for recovery of a neat powder, a washing step is essential.
(3) In the use of the powder or beads as a component of a coating, the residual protective colloid acts as a binder to lower the dispersibility of the particles.
The prior art manufacturing technologies have these additional drawbacks.
(4) The prior art requires a special emulsifying machine, such as a homogenizer, colloid mill or homodisperser.
(5) Anionic, cationic or amphoteric particulate polymers cannot be produced.
(6) In dispersing the particulate polymer in a coating material or solvent suited to the intended application, even the use of a dispersing agent does not insure good dispersibility.
(7) The particulate polymer is are poor in heat resistance and solvent resistance.